1. Field of the Invention
The present invention generally relates to a parachute with a skirt reefing system.
2. Description of the Related Art
Large cargo parachutes typically have diameters of about one hundred feet and are made of solid cloth. Due to the large amount of canopy fabric, the opening process of such relatively large cargo parachutes is typically controlled in order to allow the canopy to open in stages thereby ensuring proper and safe inflation. A common technique used to control the opening process of the canopy is skirt reefing. Skirt reefing involves the use of a reefing line or cord with a length that is less than the circumference of the canopy skirt when the canopy is fully opened. The reefing line is attached to the skirt by sliding it through the reefing rings permanently attached to the canopy skirt at each suspension line junction. During initial parachute opening, the skirt opens to a circumference defined by the length of the reefing line thereby controlling and retarding the opening process. After this initial stage of parachute opening, the reefing line is then cut by pyrotechnic cutters which have preset firing times. Once the reefing line is cut, the skirt is released and the canopy continues to open. Depending on the size of the canopy and the desired degree of control of the canopy opening process, multi-stage opening can be achieved with several sets of reefing lines and pyrotechnic cutters.
FIG. 1 illustrates a prior art parachute system. Four separate reefing lines 10, 12, 14 and 16 are attached to skirt 18 of canopy 20. This prior art parachute system utilizes pyrotechnic cutter 22, 24, 26 and 28. Reefing line 10 is connected to cutters 22 and 26. Reefing line 12 is connected to cutter 22 and 24. Reefing line 14 is connected to cutters 26 and 28. Reefing line 16 is connected to cutters 24 and 28. Suspension lines 29 are connected to skirt 18. For purposes of clarity, not all suspension lines 29 are completely shown. Each suspension line 29 is connected in tandem to corresponding riser 30. In order to increase the drag force, center line 32 is connected between apex 34 of canopy 20 and the confluence point 36 wherein all risers 30 meet. Center line 32 is symmetrically located with respect to skirt 18 and is spaced from skirt 18 by radius R. Lanyard 38 connects payload 40 to risers 30. During the opening of canopy 20, center line 32 is tightly extended due to the weight of the payload 40 and the high air pressure inside canopy 20. A disadvantage of such prior art skirt reefing technique is the relatively high cost resulting from the use of a plurality of pyrotechnic cutters. The cost of such pyrotechnic cutters has steadily increased over the years and such cost contributes to the overall annual cost of conducting many cargo airdrops. For example, the U.S. Department of Defense conducts several thousand cargo airdrops using clusters of cargo parachutes every year for military and humanitarian causes. Therefore, the accumulated cost for using so many pyrotechnic cutters on these cargo parachutes is very significant.
What is needed is a cargo parachute system with skirt reefing that is relatively more economical to implement.